Method of production and arrangement of steam boilers heated by highly aggressive gases



Sept. 26, 1961 o. WOLF ETAL 3,001,513 METHOD OF PRODUCTION AND ARRANGEMENT OF STEAM BOILERS HEATED BY HIGHLY AGGRESSIVE GASES Filed Aug. 9, 1954 BURNER INVENTORS 0110 WOLF,

WALTER WENZEL, 74 73 75 KARL SCHMIDT,

RUDOLF HEQENS TH z WERNER HULSSEP ROLF DORLIN&.

MTT

THEIR ATTORNEY.

3,001,513 METHOD OF PRODUCTION AND F STEAM BOILERS HEATED BY HIGHLY AG- GRESSIVE GASES Otto Wolf, Walter Wenzel, Karl Schmidt, Rudolf Hellenstreit, Werner Hiilsse and Rolf Diirling, Gummersbach, Germany, assignors to L. & C. Steinmiiller G.m.b.l-I.,

Gummersbach, Germany Filed Aug. 9, 1954, Ser. No. 448,626 4 Claims. (Cl. 122-7) The invention relates to an operating process and the structure of steam boilers which are heated by highly aggressive gases, e. g. gases which contain much sulphuric or nitric oxide. Such gases are produced especially by roasting or sinten'ng furnaces and by chemical plants; however, they can also be formed directly during the firing of the steam boiler itself by the combustion of e.g. solid, liquid or gaseous fuels of high sulphur content.

The roasting gases, in particular, contain considerable quantities of heat which are lost if they are expelled into the atmosphere or are exploited immediately for their chemical content. Thus designers have long been trying to extract the heat content from these gases asfar as possible beforehand. The problem is, however, that e.g. owing to their high sulphuric oxide content these gases have a very high condensation point, so that normal waste heat boilers, under the normal operating conditions, are very rapidly destroyed owing to the strong acids which form on condensation.

Taking these facts into account, the invention provides that all iron or metal parts of the boiler insofar as they can be attacked by the hot gases be kept, during operation, with certainty above a temperature which exceeds the point of condensation of this heating gas, using either the hot gases themselves or outsideheat sources such as steam from other boilers, other, non-aggressive waste gases, or supplementary firing.

Since the greater part of the structural parts containing iron is represented by the heating surfaces of the boiler itself, it is particularly suggested, in view of the temperature of the vaporizer heating surfaces, to keep the boiler pressure constantly above a certain minimum value where the saturation temperature of the. water or steam is above'the condensation point of the heating gases.

It is also important to prevent access of cool air from outside, since this causes local cooling of iron parts which may simultaneously be in contact with the heating gases. As a means to this end the gas pressure in all boiler flues may advantageously be kept above the ambient air pressure, for which purpose the flue-gas slide installed especially at the end of the boiler, or control valves, can be used in a basically known manner.

In order to maintain the boiler pressure it is advisable to install a relief valve in the steam extraction pipe. This valve allows steam to flow only as long as the boiler pressure remains above the admissible lower limit. The boiler pressure thus maintains a certain minimum value, without reference to the required steam output.

When certain safety measures are observed there is a possibility of using air or feed-water p-reheaters. The safety measures in question consist essentially in maintaining the inlet temperature of the medium to be heated without fail above the point of condensation of the heating gases, by one of the known methods. Should the temperature fall below the required water or air temperature a three-way or butterfly valve connected in front of the preheater can be actuated, which conducts the water directly to the boiler drum and the air directly, or via an otherwise heated prcheater to the fire.

In order to seal off the boiler as reliably as possible so as to prevent both escape of heating gasm and entry of cool air, it is suggested that the boiler be furnished with ARRANGEMENT nited States Patent 6 "ice a thoroughly hermetic plating disposed between an inner and an outer layer of insulation.

The purpose of this two-sided insulation is to maintain the steel plating with certainty at a temperature above the admissible minimum temperature, e.g. at approximately 300 to 350. In order not to raise this temperature needlessly and to maintain it with both high and low heating gas temperature, the inner insulation must be considerably more effective, for example, at the boiler in. let than at the end of the boiler, where, on the other hand, the outer layer of insulation must be correspondingly thicker.

Obviously, a similar measure may also be applied for the parts of the boiler housing which are in contact with the heating gases.

With reference to the dust separators or gas cleaners which are usually employed for further exploitation of the roasting furnace gases and which require a minimum operating temperature of approximately 300 to 350, the flue gases at the end of the boiler must also maintain this temperature. For this purpose, e.g. in an essentially known manner, a part of the boiler heating surfaces can be circumvented by means of a by-pass duct or by-pass valve on the flue gas side, depending on the requirements.

In order to be certain of avoiding the dangerous condensation processes and acid formation even during the starting up of a boiler which has cooled off, it would appear necessary to heat the entire boiler in advance, by means of external heat sources, to a temperature above the admissible minimum temperature. For this purpose the means already mentioned can be employed, e.g. heating by means of outside steam, by means of other, nonaggressive waste gases, and especially by starting up a small, supplementary firing device, e.g. an oil or gas burner, or the like, installed in front of the boiler inlet.

A similarly corresponding measure is necessary when shutting down the boiler, as soon as the heating action of the aggressive gases is no longer sufiicient to guarantee the minimum temperature for all parts of the boiler. These measures must be maintained until the last traces of aggressive gases have left the boiler.

It appears inadvisable to employ the usual method of cleaning the external boiler heating surfaces by means of steam or compressed-air blowers, since these may through the porous insulating and building materials of the. waste heat boiler and the action of thesefgases on the cooled metal parts, the following additional suggestions are made for increasing the impermeability of the boiler walls and at the same time facilitating and speeding up the work of assembly and repairing:

The boiler jacket is always in contact with the heating gases in such a way that the insulation, which may take the form of bricks, stuffing material or fabric mats, lies behind this plating in order to prevent the gases from reaching it. The plating can be placed in front of or behind the wall-cooling pipes, depending on the circumstances.

The drawings show an embodiment of the subject of the invention and specific improvements.

FIGURE 1 represents a vertical, longitudinal section of the boiler,

FIGURE 2 the corresponding ground plan, and

FIGURE 3the -longitudinal and lateral views of a pro- V tective hood for the tubes.

Through the entrance duct 1 with auxiliary burner 2, installed for supplementary firing, the heating gases (from the roasting furnace which is not shown) enter the boiler and first come into contact in the descending flue with evaporator surface 3, then ascending, with superheater 4, and descending again, with the second evaporator surface 5, after which they pass out through exit duct 6 with flue control valve 7, going to thefollowing dust-removal plant (likewise not shown). Dust separating cones 8 and 9 are placed below the lower points of gas reversal between heating surfaces 3 and 4, and also and 6. By means of by-pass valve between these two points of reversal, heating surfaces 4 and 5 can be partially circumvented on the gas side, in order to keep the gas temperature in duct 6 at the necessary high value. Of course, in order to avoid influencing the superheat temperature involuntarily a by-pass duct can be placed parallel to the second evaporator surface, at the exit of which valve 10 may then advantageously be installed.

Under certain circumstances a bypass duct with control valve might advantageously be placed parallel to the first evaporator heating surface 3, since then, under a light boiler load (low flue gas exit temperature) the superheating would be automatically sustained. v On the tubes against which the heating gas flows frontally replaceable protective caps 11 (represented in the drawing by broken lines) may be mounted, designed e.g.' in U-shape or trough-shape according to FIGURE 3. In addition, e.g. in the first upper gas reversal section, protective plate 12 can be mounted in front of the tubes receiving the direct flow.

Plating 13, which seals olf the boiler, is placed between the inner layer of insulation 14 which decreases in thickness with the heating gas temperature and the outer layer of insulation 15 which increases correspondingly.

In thedrawing the boiler is represented as a forcedcirculation boiler with evaporation drum 16 and circulation pump 17. The feed water enters the upper drum at 18. A gas-heated feed-water preheater is not furnished since such a device is only economical with high boiler pressures. The ovelflow valve 19 governing the downward limit of the boiler pressure is installed in the hot steam exit duct. The jolting device for cleaning the heating surfaces is not shown.

What we claim is:

1. A steam boiler installation adapted to be heated by strongly aggressive gases having a high condensation point and an ingress temperature above said point, said boiler installation comprising several flues arranged parallel to each other and to be passed in succession by the heating gases, the first flue including evaporator surfaces, the second superheater surfaces and the third again evaporator surfaces, said heating sur fiaces forming parts of a steam generating plant, dust separating cones disposed below the lower points of the an inlet duct for the admission of the heating gases into the boiler, an outlet duct for the gases, a flue gas reversal,

control valve in the outlet duct, metal walls covered with an impervious coating enclosing said fines, and an inner layer and an outer layer of insulation disposed on opposite sides of said walls, said layers maintaining the temperature of the underlying metal walls at all points thereof at a predetermined value above the condensation point of the heating gases.

2. A steam boiler installation according to claim 1, comprising adjustable by-pass means on the gas side for circumventing some of the heating surfaces in a controllable manner whereby the waste-gas temperature at the end of the boiler can be held above a certain minimum value.

3. A steam boiler installation according to claim I, wherein individual groups of said heating surfaces are slidable into and out of the gas how for controlling the heat applied to them by the flue gases.

4. A method of operating and shutting down a steam boiler adapted to be heated by strongly aggressive gases having a high condensation point, said boiler including metal parts subject to contact with and corrosion by said gases, said method comprising the operating steps: applying an auxiliary heating medium to said metal parts to raise the temperature thereof above the condensation point of said heating gases, admitting said aggressive gases into the boiler when said metal parts have reached a temperature above the condensation point of said gases, applying continuously to all said metal parts of the boiler in contact with the gases a heating medium'at a temperature above the condensation point of said aggressive gases for maintaining said metal parts above said condensation point while in contact with said gases, and discon-' tinuing the admission of said aggressive gases into the boiler when the temperature of said metal parts falls below the condensation point of said gases; and the shutting down steps: comprising heating the entire boiler to a temperature above said condensation point by supplying supplemental external heat, discharging the aggressive gases during such supplemental heating and when the boiler is at said temperature, continuing the supplemental heating until the last aggressive gases have References Cited in the file of this patent UNITED STATES PATENTS I OTHER REFERENCES The Efiicient Use of Steam (Lyle), published by His Majestys Stationery Ofiice (London), 1947 (pages 742 and 743 relied on). 7

left the boilers 

